The present invention relates generally to a stent retrieval device, and more specifically to a stent retrieval device for retrieving a misplaced stent.
Stents are used in a wide variety of medical procedures such as percutaneous transluminal angioplasty (PTA), percutaneous transluminal coronary angioplasty (PTCA), and many other well known procedures. There are several types of stents, including balloon expandable stents and self-expanding stents. Examples of balloon expandable stents are disclosed in U.S. Pat. No. 4,733,665 to Palmaz, U.S. Pat. No. 5,449,373 to Pinchasik et al and PCT WO 96/03092 to Israel. An example of a self-expanding stent is disclosed in U.S. Pat. No. 5,037,427 to Harada. These stents can be delivered using a wide variety of medical devices, including over the wire (OTW) catheters, single operator exchange (SOE) catheters and fixed wire catheters.
Balloon expandable stents are typically carried on a non-compliant balloon, which is inflated at high pressure to expand the inside diameter of the stent, forcing it against the vessel interior walls. A typical balloon expandable stent requires a pressure greater than 2 atmospheres to overcome the expansion force threshold of the stent. Balloons are classified as compliant, semi-compliant and non-compliant. For purposes of this application a non-compliant balloon will radially expand 2-7% greater than its nominal diameter at 6-12 atmospheres; a semi-complaint balloon will radially expand 7-16% greater than its nominal diameter at 6-12 atmospheres and a compliant balloon will radially expand 16-40% greater than its nominal diameter at 6-12 atmospheres. See U.S. Pat. No. 5,556,383 to Wang et al for a discussion of balloon compliance. Also for purposes of this application a non-compliant balloon has a flexural modulus of greater than 250,000 psi; a semi-compliant balloon has a flexural modulus of between 180,000 and 250,000 psi and a compliant balloon has a flexural modulus of less than 180,000 psi.
During a medical procedure a stent can become misplaced, either due to improper location, failure to expand properly, partially dislodge from the balloon or completely dislodge from the balloon. One common problem is caused by the stent contacting a guide catheter and becoming completely dislodged from the balloon. In such as case, a self-expanding stent which fails to expand fully or a balloon expandable stent which has not been expanded is loose in the vasculature.
Often for lack of any other alternative the physician attempts to utilize a typical balloon catheter to retrieve the stent. In this case typical means a non-compliant balloon which must be operated at high pressure. Since most stents can be expanded by exceeding their expansion force threshold with a pressure greater than 2 atmospheres, using a typical balloon can be problematic and the retrieval is often unsuccessful.
What is needed is a stent retrieval catheter with a specialized balloon which allows for retrieval of a stent which has been misplaced without the danger of expanding the stent during the retrieval operation.